1. Field of the Invention
The present invention relates to an anti-fogging coating material which is capable of imparting hydrophilicity and the function of absorbing water to the surfaces of substrates, such as optical lenses, spectacles and window glass of vehicles, which require anti-fogging properties and the prevention of dew condensation, and the surfaces of films for bubble-jet printers, and forming a water-insoluble film having a high surface hardness, an anti-fogging coating film formed out of the anti-fogging coating material, and an anti-fogging article on which the anti-fogging coating film has been formed.
2. Related Background Art
The reason why substrates such as glass and plastics fog up is that moisture in the air adheres thereto in the form of fine waterdrops because their surface temperatures are lowered to a dew point or lower, and so light is irregularly reflected on the surfaces of the substrates. Accordingly, it is considered that the occurrence of fogging can be prevented by preventing the formation of waterdrops on the surfaces of the substrates. As such anti-fogging methods, for example, four factors of (A) adjustment of wetting; (B) impartment of water-absorbing properties; (C) impartment of water repellency; and (D) adjustment of humidity by heating have been considered.
With respect to the factor (A), anti-fogging sprays and the like are on the market for the purpose of adjusting wetting, namely, making a contact angle between a substrate and a waterdrop small. However, such a spray uses a surfactant or the like, so that the durability of its effect is not good.
With respect to the factor (B), the water-absorbing properties is an effect brought about by a coating film of a hydrophilic polymer, and the durability of the effect is somewhat good when compared with the anti-fogging spray. However, a substrate to the surface of which the water-absorbing properties have been imparted by such a coating film fogs up when exceeding the water absorption capacity of the coating film, and the surface begins to dissolve.
With respect to the factor (C), the water repellency is imparted by applying a water-repellent compound to a substrate. When the water-repellent compound is applied to, in particular, the inside surface of a vinyl plastic hothouse, fine waterdrops on the surface come into contact each other and fall as bigger waterdrops, whereby anti-fogging properties can be developed. However, fine waterdrops may adhere to the surface in some cases, resulting in the occurrence of fogging.
With respect to the factor (D), the adjustment of humidity by heating can achieve an anti-fogging effect on lenses of copying machines, rear windshields for automobiles and high-grade dressing tables. Since a power source is required, however, its application fields are limited.
Further, the films formed out of an anti-fogging coating composition comprising an organic polymer containing a surfactant have been developed. This anti-fogging coating composition is so designed that the film formed is made hydrophilic by polyether polyol in the presence of the surfactant to absorb moisture, and wetting is adjusted by the surfactant contained when the moisture exceeds the critical point of water absorption of this film, thereby retaining good transparency. Since the surfactant is easily dissolved in water and dissolved out, however, the anti-fogging properties and strength of the film are markedly lowered.
Japanese Patent Application Laid-Open No. 8-231944 discloses that the drawbacks involved in the conventional methods are improved by using polyalkylene oxide and a polyacrylic as organic polymers, and making use of a three-dimensional structure formed by the hydrolysis and polycondensation reaction of an inorganic alkoxide. However, a problem arises after immersion in water for a long period of time and upon use at a low temperature, and so there is a tendency not to sufficiently develop its performance.